This invention relates to an implantable heart pacing and monitoring system. More specifically, this invention relates to a system which produces an intracardiac electrogram and transmits the electrogram to monitoring instruments external to the patient. Further, this invention relates to an associated method for heart pacing and monitoring.
The use of heart pacers, commonly called "pacemakers", is well known in the art. Such devices include a pulse generator which stimulates the patient's heart by use of one or more pacing-sensing electrodes.
The evaluation of pacer function is considered mandatory for the health and well being of the patient. As pacemaker or pacer longevity increases, better and more sophisticated follow-up methods have become available. The telemetric monitoring of such diverse pacemaker functions as output voltage and current, rate, end of life indication, refractory periods and delays are becoming common. The ordinary surface electrocardiogram is still relied upon to differentiate the arrhythmias produced by the pacemaker from abnormal pacemaker function. This task has become increasingly complex with the development of dual chamber and the so-called physiological pacemakers. The multiple modes of pacing and having pacers being "committed" and "non-committed" have produced a wide array of ecg (electrocardiograph) changes which can make interpretation of pacemaker function difficult. Monitoring has progressed from a simple lead II electrocardiogram to a minimum of six leads for ventricular pacing to a full 12 lead ecg for dual chamber pacers. Echocardiographs have even been required to aid in determination of capture in some difficult cases. All of these techniques are time consuming and expensive for the patient.
The ability of pacing electrodes to sense and detect normal intrinsic cardiac electrical activity is well known. These electrodes are adequate, in most instances, for the detection of the normal non-paced electrocardiogram. Telemetry systems incorporating such sensing systems have heretofore been used. Such systems cannot, however, be used to detect the electrocardiogram immediately following a stimuli originating from that electrode. The high output spike, after-potential, and electrode-tissue polarizations render the electrode blind to the induced electrocardiogram. Furthermore, since the sensing circuit gain is tuned for the relatively low voltages of the heart (3-4 mV for the atrium, 10-20 mV for the ventricle), the thousand-fold higher output levels produced by the pacemaker must be blocked from the sensing circuit by blanking and refractory periods so that the pacer is not disabled to subsequent electrial activity. In other words, the pacing-sensing electrodes are temporarily blinded in somewhat similar fashion to dark-adapted eyes being suddenly blinded by a very bright light. It is not even possible to try to determine a capture electrocardiogram until long after the intrinsic waveform has moved well away from the pacing spike. Therefore, a system which uses the same electrode for pacing, sensing, and telemetry may only generate a complete electrogram when the pacemaker is not pacing. This negates the use of a just one electrode telemetry-pacing system in all single chamber and any dual chamber pacer where both chambers may be paced.
The detection of the intracardiac electrogram by a single electrode separate from the pacing-sensing electrode is disclosed for example, in U.S. Pat. No. 4,387,717 issued June 14, 1983 to Robert R. Brownlee, Howard C. Hughes, Jr., Paul H. Neff, and G. Frank O. Tyers, entitled "Pacer Internal Cardiac Electrogram Sensing System", and this patent is hereby incorporated by reference. Although this system is capable of detecting the electrogram during both intrinsic and paced beats, it lacked the ability for high resolution electrogram detection from both chambers simultaneously. The single, separate electrode was used to pick-up both P and R waves.
The following incorporated by reference patents are further representative of other arrangements for heart pacing:
______________________________________ U.S. Pat. No. Inventor Issuance Date ______________________________________ 3,662,759 Dabolt May 16, 1972 3,825,015 Berkovits July 23, 1974 3,977,411 Hughes, Jr. et al Aug. 31, 1976 4,142,533 Brownlee et al Mar. 6, 1979 4,355,642 Alferness Oct. 26, 1982 4,374,382 Markowitz Feb. 15, 1983 4,394,866 Hughes Jul. 26, 1983 ______________________________________
The Dabolt patent discloses a pacemaker which produces artifacts for detection upon a traditional EKG machine. These marker pulses indicate whether the pacemaker has sensed the normal intrinsic activity.
The Berkovits patent discloses pacing the heart through exposed ring electrodes. The electrodes are bipolar meaning that the rings in each of separate heart chambers are designed to be used as pairs, one ring serving as the cathode and other ring serving as the anode. The ring electrodes are used for atrium-ventricle sequential pacing.
The Hughes et al U.S. Pat. No. 3,977,411 describes a cardiac pacer system and method where an electrode with a relatively large surface area is used for sensing cardiac activity, and a second electrode in contact with the myocardium is used for applying the stimulator pulses to the heart. Both electrodes are unipolar, and the sensing electrode is used for controlling the pacemaker electronics and detecting R-wave activity.
The Brownlee et al U.S. Pat. No. 4,142,533 discloses a system for telemetering and monitoring the function of an implanted pacemaker. The telemetry is by digital signals.
The Alferness patent discloses a detecting electrode constructed for attachment to the surface of a patient's heart. This type of electrode would not normally be implanted through the vascular system, but instead would be implanted transthoracically. This electrode system would be used for looking at a very limited area of the myocardium (viz., area between the electrodes) to detect ventricle electrical activity.
The Markowitz patent discloses a pacer circuit incluing a telemetry system. The telemetry system generates a series of pulses which simply indicate whether an event has been detected by the pacemaker circuit and if the pacemaker circuit has responded to the event. The system uses the pacemaker's pacing-sensing electrodes for this detection.
The Hughes U.S. Pat. No. 4,394,866 discloses an S-A node helical lead for use with atrial pacemakers. The tip of the lead is placed at the area of the S-A node for optimal detection of the P-wave by the pacemaker and for generating the stimulating pulse or pacing through the same conductive member.
Although the discussed pacing systems have been generally useful, they are commonly subject to one or more of a number of problems or limitations in applicability.
The heretofore discussed designs have been unable to telemeter a reliable and complete intracardiac electrogram (EGM) during the pacing operation. Generally therefore, the examination of the pacer performance and capture still ultimately rely upon an external or surface electrocardiogram (EKG) which may be extremely difficult to monitor and interpret due to such factors as retrograde conduction, fusion, pseudo-fusion, and confusion concerning programmed settings.